1. Field of the Invention
The present invention relates to an antenna system for receiving and transmitting wireless signals, especially relating to an antenna system capable of improving nonlinear distortion of signals.
2. Description of the Prior Art
When a practical antenna system is transmitting signals, a certain amount of power distortion is inevitable. For example, an antenna system transmits a 1 dBm (decibel milliwatt) signal, if power loss of the antenna system is 0.5 dBm, output signal of the antenna system will be 0.5dBm. However, nonlinear distortion may occur in antenna systems when transmitting higher power output signals. For example, when the antenna system transmits a 10 dBm signal, the power loss is increased to 1.5 dBm from the former 0.5 dBm, thus the output signal will be 8.5 dBm. This causes distortions to occur in signals.
FIG. 1 is a diagram showing curves of output power relative to input power of antenna systems, wherein the inclined dotted line represents a curve without distortion of output power (Pout) relative to input power (Pin), and the solid line represents a curve with distortion of Pout relative to Pin. When the difference between Pout without distortion and Pout with distortion reaches 1 dBm, the corresponding Pin is so-called P1dBm. When a signal's Pin reaches P1dBm, distortion of its output signal could be severe. Therefore, distortion extent of output signal can be determined when Pin reaches P1dBm. Besides, if P1dBm is enhanced with reduced interference and parasitic effects, Pout will reach P1dBm point until higher power, thus improving nonlinear distortion of the signal.
Integrated Passive Components (IPCs) are attracting an increasing interest due to needs of handheld wireless devices to decrease in size and cost and increase in functionality. Many functional blocks such as impedance matching circuits, harmonic filters, couplers, baluns and power combiner/divider can be realized by IPCs technology. IPCs are generally fabricated using standard wafer fab technologies such as thin film and photolithography processing.